Lens brands
 

So there's Canons, Nikons, Sigmas, Tamrons, and a few others. Is there a premium on Canon branding? Which brands tend to provide best buck bang?

Almost everyone ends up with mostly Canon after several years. Not that most people don't have a favorite non-Canon lens - for me it's the Nikon 14-24mm. Below 35mm is the area where Canon is the weakest.

Why is that? Presumably you pay a premium for the brand?

When you buy anything, you're paying for that company's activities: marketing, promotion, sponsorship, and of course the hardware itself. Companies like Tamron and Sigma don't advertise or sponsor as much as Canon, so that's a factor.

It sure seems like quality assurance is another significant variable. Canon itself produces "bad copies" of lenses, but I've bought six and I've never had a bum lens. I'm not definitively saying that Tamron and Sigma have worse QA, but this could be a factor.

As was stated before, every lens manufacturer has their own high-end models, one or two insane-value models, and a few straight-up lemons, and that includes Canon. Tamron and Sigma have a few models that are very popular for solid reasons. FredMiranda.com has a great reviews section that can help you get a better sense of the EF-mount lens landscape from other photographers' points of view.

All that said, I own Canon glass (all L series), although a 50mm Zeiss and a lensbaby are coming to be paired up with a 7D. But YMMV.

Not necessarily. Sigma's new 50mm 1.4 lens costs $499...Canon's 50mm 1.4 is going for $100 less. (By the way, Sigma's lens may be better than Canon's.)

Sometimes off-brand lens makers will allow the aperture to open further than Nikon or Canon would with the same glass. Take an f/4 lens from a major brand. A 3rd party might let the aperture open to f/2.8. The result is bad falloff and soft corners at f/2.8. At f/4 and above, the performance could be similar for both lenses. Because of the f/2.8 specification, the 3rd party lens looks better on paper.

I recommend looking closely at the falloff charts in lens reviews before buying any lens - especially any 3rd party lens. You might find a bargain. But you also might find that your f/2.8 lens isn't viable until f/4 or f/5.6.

Be aware that Canon reserves its automatic vignetting correction on the 7D video for its lenses only, all other brands will be left uncorrected.

Nikon is the most expensive. Most Nikon lenses can be matched by a Canon that is around three quarters of the price. Notable exceptions include unique lenses such as the 14-24 f/2.8 and 200-400 f/4.

There are some real gems among the Sigmas, Tamrons, Tokinas, et al. Autofocus is where these lenses often go wrong, but if you're only using them for video, that will not be an issue. Sometimes they have reliability issues in other areas (I.S., zoom mechanism, barrel separation, etc.), though. Check out these pages from Roger Cicala:

LensRentals.com - The Sigma Saga

LensRentals.com - Lens Repair Data 3.0

So if you don't need autofocus, the off-brand lenses easily provide the highest buck-bang. You can get the similar optical quality for 25-50% cheaper. For example, the Tamron 17-50 f/2.8 VC has the same performance and features as the Canon 17-55 f/2.8 IS, but is $650 instead of $1,000. The macro lenses are another area where Canon is bested in buck-bang.

The 24mm f/1.4 L II is the notable exception: no one else even attempts such a fast wide except Leica.

This is only true if one considers buying new current model lenses. Many older manual Nikon lenses are a real bargain on the used market.

That's a great point. Thanks for the correction.

It's good to note with the LenRental data, that shipping the lenses themselves has been a source of repairs. They noted that the Sigma 120-300/2.8 had a very high repair rate due to how it was packed and shipped. I have the same lens, and it was first owned by a PJ, so it's been thru some rough handling, but it works very well.

If you need to travel alot with your gear, this is probably a very important data point, if not, then you'll need to factor that in before dismissing it.

And Canon is resetting the price of its better lenses to be closer to Nikon. The generalities about Canon and Nikon pricing aren't necessarily true outside the U.S.

Canon has for a long time made more lens types than Nikon, but Nikon is catching up. Both are producing the best glass ever, but both stumble on some lenses too. Canon big glass is still significantly less expensive than Nikon. Canon big glass is generally available while Nikon has more shortages.
Nikon used to be terrible about producing enough popular lenses. But they have improved. Competition is good.